I use 12 or 15 GB for the C-drive for most VM's. If it's a Citrix, most of the time it's 30 GB because of userprofiles (although they can be relocated).

About paging file: I prefer fixed paging files of at least the size of RAM you have assigned the VM. Windows will always put things in the pagefile even if it has enough memory. If the .vswp-file is being used by ESX for the VM, then performance will drop dramatically...the paging file in windows can be used but of course it shouldn't be used continuously.